Partysip is an implementation of a SIP proxy server. SIP stands for the
Session Initiation Protocol and is described by the rfc2543 (soon to be
deprecated by latest revisions). SIP is a open standard replacement from
IETF for H323.

Partysip is a modular application where some capabilities are added and
removed through plugins. The program comes with several GPL plugins. At
this step, partysip and its plugins could be used as a 'SIP registrar',
a 'SIP redirect server' and a 'SIP statefull proxy server'. (stateless
capabilities have been removed)

WWW: http://www.partysip.org/